Vehicle occupant protection systems, which are activated in response to a vehicle crash, for the purpose of mitigating occupant injury are well known in the art. A vehicle may contain automatic safety restraint actuators such as front and side air bags, seat belt pretensioners, and deployable knee bolsters. The occupant protection system may further include a collision/crash sensor for sensing the occurrence of a vehicle crash and for providing an electrical signal indicative of the crash severity.
Several known occupant protection systems include an occupant classification or weight detection system. The occupant classification/weight detection system could consist of occupant size or weight determination on force/load sensors, capacitive/electric field sensors, resistive load distribution sensors, ultrasonic sensors, infrared sensors, and/or image based sensors. A controller, which is connected to one or a combination of these sensors, controls the inflatable protection module in response to the sensed size or weight of the occupant. In response to the sensed occupant size or weight, one or more deployment aspects of the air bag may be adjusted. A protection system with adjustable aspects of deployment is commonly referred to as an “adaptive” protection system. Specifically, if the occupant is so small or light that deploying the air bag will not enhance protection of the occupant, it may be desirable to suppress actuation of the occupant protection module. In such a case, deployment may even be more detrimental than no deployment at all.
In any case, the determination of an occupant's size or weight is an important part of adaptive occupant protection systems. There are several types of size classification or weight determination systems. A system that classifies the occupant based on the strength of an electric field (or the capacitance of the human body) may be fooled if a portion of the signal used to excite the sensor is lost. A system that classifies the occupant based on the load distribution, size, shape and/or orientation of the occupant's posterior may not be reliable because varying people of varying heights and weights may have posteriors with similar size and shape characteristics. A system that relies solely on force/load sensors cannot account for false readings due to external forces such as accelerations or losses due to body angle or foot position. Different obstacles such as a map, a book, or a newspaper could occlude signals from ultrasonic and video based systems. A lighter or cigarette could blind an infrared-based system.